1. Field of the Invention
The present invention relates to an image recording substrate for use in electrophotography and more particularly to an image recording substrate used as a photosensitive drum for internal irradiation electrophotographic apparatus such as copiers, laser printers and the like.
2. Description of Related Art
Hitherto, many photoconductors used in recording apparatuses such as copiers, laser printers and the like include an aluminum substrate as a photosensitive drum or photoconductor, and generally such photoconductors are exposed from above the front surface of the photosensitive layer provided on the substrate in an exposure process.
In this exposure method, apparatuses used in various steps such as charging, exposure, development, image transfer, fixing, static elimination, and cleaning have to be arranged around the photosensitive drum of an electrophotographic apparatus. This poses a limitation on trials for down sizing of recording apparatuses and could cause developers to dissipate from the developing apparatus, thus contaminating the optical system included in the exposing apparatus to adversely affect the quality of printing.
A conventional approach for solving these problems was to provide an internal irradiation type electrophotographic apparatus which includes a photosensitive drum comprising a transparent substrate having coated thereon an electroconductive layer and a photosensitive layer and a light source for exposure arranged inside the drum as a photoconductor so that the apparatus can be rendered down sized and the contamination of the optical system by dissipation of the developer can be prevented.
In the manufacture of photoconductive drums used in such an internal irradiation type electrophotographic apparatuses, there has been used a technique in which indium tin oxide (hereafter, abbreviated as "ITO") or the like is deposited by sputtering or vacuum deposition in order to form a transparent electroconductive layer on a transparent substrate such as inorganic glass or the like. Japanese Patent Application Laying-open No. 319195/1995 (Fujitsu) discloses a photosensitive drum comprising a cylindrical glass substrate having superimposed thereon a doped polyaniline.
The-above described conventional approaches have problems that cylindrical inorganic glass substrates are expensive, poor in dimensional precision, and fragile, and film formation of the transparent electroconductive layer by sputtering or vacuum deposition is poor in productivity and the step of forming a doped polyaniline layer is costly.
The features required for substrates for use in internal irradiation type electrophotographic apparatuses include low cost of materials to be used, high dimensional precision, sufficient mechanical strength for photosensitive drums, chemical stability not to deteriorate its quality as a photosensitive drum even in an uncontrolled open air, enough transparency to allow irradiation to transmit without refraction upon exposure, high adhesion with the transparent electroconductive layer on the substrate, solvent resistance and heat resistance required when forming a photosensitive layer by dip coating, which is highly productive, and the like.
On the other hand, the features that transparent electroconductive layers must have include low cost, transparency upon exposure, i.e., allowing irradiation to pass through without refraction, appropriate surface resistance within the ranges that allow use as a photosensitive drum, and the like. There has been a demand for the development of an improved photoconductor for electrophotography in these and some other respects.